Extreme Cold and Cold in Illinois, February 13 to 14, 2021

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
545 PM CST Sat Feb 13 2021

.SHORT TERM...
123 PM CST

Through Sunday...

Snow will taper rapidly from west to east over the next few hours
leaving behind a wide swath of 1 to 4 inches over northern Illinois
and northwest Indiana. Snow totals hit the 6 inch mark along the
lakeshore of northwestern Indiana thanks to an overnight boost from
a lake effect snow band.

Tonight, clouds will clear and temperatures will take a nosedive.
Overnight lows of 5 to 10 below zero are expected areawide, with
locally colder readings likely. With a stout pressure gradient
remaining in place keeping northwesterly winds of 10-15 mph,
dangerously cold wind chills of 20 to 35 degrees below zero are
expected with the coldest values from the Fox Valley westward and
"warmest" in northwestern Indiana. The coldest and most dangerous
time period will be toward daybreak with we reach our diurnal
minimum in temperatures. With clouds expected to increase after
daybreak Sunday, we won't have much opportunity to warm with
afternoon highs in the low single digits expected. In fact, some
spots west of I-39 may not climb above zero! Wind chills will
remain cold during the day on Sunday with readings in the teens
below zero. Sunday night, wind chill values may slide back down to
twenty below, continuing the dangerous cold stretch.

We may sound like a broken record, but don't let your guard down
with the cold. Be sure to bundle up from head to toe in multiple
layers when heading outdoors.

Borchardt

&&

.LONG TERM...
1259 PM CST

Sunday night through Saturday...

The snowy and cold pattern will still have its grips on the region
this upcoming week with several rounds of mostly lighter snow
embedded with a strong signal for lake effect snow, both across
northwest Indiana and portions of northeast Illinois in the late
Sunday night - early Tuesday time frame.

The upper level pattern will feature a cold low over the upper
Midwest, with a longwave trough over a vast majority of the country
which has led to widespread wintry weather across much of the USA.
Embedded on the southern/central periphery of the trough are several
disturbances that will percolate northeast across a lingering
baroclinic zone. That baroclinic zone is anchored in place with
strong surface high pressure across the upper Midwest that extends
northeast to Lake superior. As each of these disturbances move along
the frontal region, we note some tightening of the frontal zone and
an associated significant strengthening of the upper jet across the
area. The first wave appears to tighten more over the local area
centered on the overnight hours Sunday night into Monday.

The second stronger disturbance across the southern periphery of the
cold upper trough, which at this point extends all the way to the
Gulf of Mexico, will shift across the Tennessee valley Monday night
into Tuesday. While there is good model agreement that the stronger
jet forcing and QPF will be focused farther southeast with this
system, a northern extension/subtle trough in the 500/700 mb layer
should easily lead to another round of light snow for areas
south/east again during this period.  There is more disagreement as
to the extent that this will occur.

The strong surface high across the upper Midwest during each of
these system will play a big role in additional snow due to lake
effect processes. The orientation of the high and associated wind
response look to keep northwest Indiana in the crosshairs for what
could be some decent lake effect snowfall. There are several models
that show a good convergence signal/mesolow development across
southern Lake Michigan. At this distance Sunday overnight has the
focus in NW Indiana, and then shifting into Cook County IL
(especially southern Cook) Monday morning.  As the next disturbance
moves along the frontal zone Monday, the mean 1000-850 wind and
surface pattern remains locked and could keep the lake effect
focused a bit longer, which could be a bit more concerning for
western Lake IL and portions of Cook county IL. Wind shear does tend
to be somewhat limited which is also a favorable for snow band
development. Thermodynamically, things are clearly quite favorable
as well given then even colder airmass, Lake induced CAPE is present
too, and even with equilibrium levels not too high, the lower
portion of the soundings will be in prime snow production region.

Needless to say, this could end being our most significant impact
from these next few systems given this signal, and even our national
blend of models mean forecast has over 6" of snow forecast in Gary,
IN with these events (maybe a mix of lake effect and synoptic
snows).

Low level flow will turn to the southeast or maybe east later
Tuesday into Wednesday. This will ease the cold a touch, but will
also contribute to some "warm advection" ahead of another system
in the southern stream slated for the later Wednesday/Thursday
time frame which could give the area yet another round of snow.

Looking beyond, we will ultimately turn our low level flow around to
southwesterly late in the week as the cold upper low will make its
exit. The positive note is temperatures could get close to the
freezing mark! And  while we get a brief precipitation break, the mid
and upper flow will become fairly progressive, thus occasional snow
chances may return at some point in the upcoming weekend.

KMD

&&

.AVIATION...
For the 00Z TAFs...

545 PM...Primary forecast concern is another period of light snow
late Sunday evening into Monday morning.

The light snow will end shortly across northwest Indiana and
clouds are clearing out. Northwest winds 10-15kts will continue
through the period with gusts into the 15-20kt range this evening.
Gusts may diminish some by daybreak and may develop again Sunday
afternoon and continue into Sunday night. These winds may cause
some minor low drifting snow tonight.

Another system will move across the southern Great Lakes region
Sunday night into Monday and is expected to spread light snow back
across the area early Monday morning, possibly starting in the
late evening. Opted to include prob mention for ord/mdw with the
new 30 hour taf due to uncertainty. A period of moderate snow may
develop before daybreak Monday. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Wind Chill Warning...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-
     ILZ012 until noon Sunday.

     Wind Chill Advisory...ILZ019-ILZ020-ILZ021-ILZ032 until noon
     Sunday.

     Wind Chill Advisory...ILZ006-ILZ013-ILZ023-ILZ033-ILZ039-ILZ103-
     ILZ104-ILZ105-ILZ106-ILZ107-ILZ108...11 PM Saturday to noon
     Sunday.

IN...Wind Chill Advisory...INZ001-INZ002-INZ010-INZ011-INZ019...11 PM
     Saturday to noon Sunday.

LM...None.
&&

Visit us at weather.gov/chicago

Follow us on Facebook, Twitter, and YouTube at:
www.facebook.com/NWSChicago
www.twitter.com/NWSChicago
www.youtube.com/NWSChicago

Hazardous Weather Outlook...UPDATED
National Weather Service Chicago/Romeoville IL
653 PM CST Sat Feb 13 2021

ILZ003>006-008-010>013-019>021-023-032-033-039-103>108-INZ001-002-
010-011-019-150100-
Winnebago-Boone-McHenry-Lake IL-Ogle-Lee-De Kalb-Kane-DuPage-
La Salle-Kendall-Grundy-Kankakee-Livingston-Iroquois-Ford-
Northern Cook-Central Cook-Southern Cook-Northern Will-
Southern Will-Eastern Will-Lake IN-Porter-Newton-Jasper-Benton-
653 PM CST Sat Feb 13 2021 /753 PM EST Sat Feb 13 2021/

This Hazardous Weather Outlook is for portions of North Central
Illinois...Northeast Illinois and Northwest Indiana.

.DAY ONE...Tonight.

Weather hazards expected...

  Significant Excessive Cold Risk.

DISCUSSION...

Dangerously cold wind chills are expected tonight, with the
coldest wind chills across interior northern and northwest
Illinois.

.DAYS TWO THROUGH SEVEN...Sunday through Thursday.

Sunday...
  Significant Excessive Cold Risk.
  Elevated Snow Risk.
Monday...
  Elevated Excessive Cold Risk.
  Elevated Snow Risk.
Tuesday...
  Limited Excessive Cold Risk.
Wednesday into early Thursday...
  Limited Excessive Cold Risk.
  Limited Snow Risk.

DISCUSSION:

Dangerously cold wind chills are again possible late Sunday night
into Monday morning.

Several rounds of snow are possible Sunday night through Tuesday.
Accumulating lake effect snow will likely impact travel Sunday night
across northwest Indiana and then shifting into portions of
northeast Illinois on Monday.

In addition to lake effect snow, areas south and east of Interstate
55 stand the best chance for hazardous travel due to snow during
this time also.

.SPOTTER INFORMATION STATEMENT...

  Spotter activation will not be necessary through tonight.

LMZ740>745-150100-
Winthrop Harbor to Wilmette Harbor IL-
Wilmette Harbor to Northerly Island IL-
Northerly Island to Calumet Harbor IL-
Calumet Harbor IL to Gary IN-Gary to Burns Harbor IN-
Burns Harbor to Michigan City IN-
653 PM CST Sat Feb 13 2021

This Hazardous Weather Outlook is for portions of the Illinois
nearshore waters of Lake Michigan and the Indiana nearshore
waters of Lake Michigan.

.DAY ONE...Tonight.

  No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Sunday through Thursday.

Sunday night and Monday...
  Hazardous conditions for small craft are likely in an around
  heavier lake effect snow showers due to gusty winds and reduced
  visibility.

Carlaw/KMD

Visit us at http://weather.gov/chicago

Follow us on Facebook, Twitter, and Youtube at:
www.facebook.com/nwschicago
www.twitter.com/nwschicago
www.youtube.com/nwschicago

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO IL
602 PM CST SAT FEB 13 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0600 PM     SNOW             ROCKFORD AIRPORT        42.20N 89.10W
02/13/2021  M0.8 INCH        WINNEBAGO          IL   OFFICIAL NWS OBS

            STORM TOTAL.

&&

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE CHICAGO IL
627 PM CST SAT FEB 13 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0330 PM     SNOW             1 E CHESTERTON          41.61N 87.05W
02/13/2021  M7.0 INCH        PORTER             IN   PUBLIC

1245 PM     SNOW             1 N PORTAGE             41.60N 87.17W
02/13/2021  M6.0 INCH        PORTER             IN   TRAINED SPOTTER

            SNOW TOTAL AS OF 12:45 PM CST.

1120 AM     SNOW             PORTAGE                 41.58N 87.18W
02/13/2021  M5.5 INCH        PORTER             IN   PUBLIC

            SNOW TOTAL AS OF 11:20 AM CST.

1100 AM     SNOW             3 N VALPARAISO          41.52N 87.07W
02/13/2021  M5.5 INCH        PORTER             IN   TRAINED SPOTTER

            SNOW TOTAL AS OF 11:00 AM CST.

0940 AM     SNOW             2 ESE VALPARAISO        41.46N 87.03W
02/13/2021  M4.0 INCH        PORTER             IN   BROADCAST MEDIA

            SNOW TOTAL AS OF 9:40 AM CST.

0400 PM     SNOW             1 SE JOLIET             41.52N 88.07W
02/13/2021  M3.6 INCH        WILL               IL   TRAINED SPOTTER

            STORM TOTAL. VIA SOCIAL MEDIA.

0432 PM     SNOW             3 SW MIDWAY AIRPORT     41.74N 87.78W
02/13/2021  M3.5 INCH        COOK               IL   CO-OP OBSERVER

            EVENT TOTAL. LIQUID EQUIVALENT OF 0.19 INCH.

0800 AM     SNOW             MINOOKA                 41.45N 88.25W
02/13/2021  M3.5 INCH        GRUNDY             IL   COCORAHS

            SNOW TOTAL AS OF 8:00 AM CST.

0350 PM     SNOW             1 NNW DOWNERS GROVE     41.80N 88.02W
02/13/2021  M3.4 INCH        DUPAGE             IL   COCORAHS

            .4 INCH YESTERDAY. 3 INCHES TODAY. SNOW JUST
            ENDED.

0700 AM     SNOW             3 NNW LAKE STATION      41.62N 87.26W
02/13/2021  M3.4 INCH        LAKE               IN   COCORAHS

            SNOW TOTAL AS OF 7:00 AM CST.

0600 PM     SNOW             OHARE AIRPORT           41.98N 87.90W
02/13/2021  M3.3 INCH        COOK               IL   OFFICIAL NWS OBS

            CORRECTS PREVIOUS SNOW REPORT FROM OHARE
            AIRPORT. STORM TOTAL. LIQUID EQUIVALENT OF
            0.13 INCH.

0800 AM     SNOW             3 NW CARBON HILL        41.33N 88.33W
02/13/2021  M3.2 INCH        GRUNDY             IL   COCORAHS

            SNOW TOTAL AS OF 8:00 AM CST.

0900 AM     SNOW             JOLIET                  41.53N 88.08W
02/13/2021  M2.8 INCH        WILL               IL   TRAINED SPOTTER

            SNOW TOTAL AS OF 9:00 AM CST.

0400 PM     SNOW             1 NNW LINDENHURST       42.43N 88.03W
02/13/2021  M2.5 INCH        LAKE               IL   COCORAHS

            STORM TOTAL. 1.6 INCH SINCE 7 AM.

1020 AM     SNOW             2 S NAPERVILLE          41.74N 88.15W
02/13/2021  E2.5 INCH        DUPAGE             IL   TRAINED SPOTTER

            ESTIMATED SNOW TOTAL AS OF 10:20 AM CST.

0900 AM     SNOW             2 WSW GOODENOW          41.38N 87.68W
02/13/2021  M2.5 INCH        WILL               IL   COCORAHS

            SNOW TOTAL AS OF 9:00 AM CST.

0800 AM     SNOW             1 SE NEW LENOX          41.50N 87.95W
02/13/2021  M2.5 INCH        WILL               IL   COCORAHS

            SNOW TOTAL AS OF 8:00 AM CST.

0800 AM     SNOW             2 S CEDAR LAKE          41.34N 87.44W
02/13/2021  M2.2 INCH        LAKE               IN   COCORAHS

            SNOW TOTAL AS OF 8:00 AM CST.

0600 PM     SNOW             ROCKFORD AIRPORT        42.20N 89.10W
02/13/2021  M0.8 INCH        WINNEBAGO          IL   OFFICIAL NWS OBS

            STORM TOTAL.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO IL
651 PM CST SAT FEB 13 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0645 PM     SNOW             BATAVIA                 41.85N 88.31W
02/13/2021  M2.0 INCH        KANE               IL   CO-OP OBSERVER

            STORM TOTAL 2.0 INCHES WITH 0.05 LIQUID.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO IL
656 PM CST SAT FEB 13 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0656 PM     SNOW             4 SSW NAPERVILLE        41.71N 88.17W
02/13/2021  M3.0 INCH        WILL               IL   PUBLIC

            .18 INCH LIQUID EQUIVALENT. SHARED ON SOCIAL
            MEDIA.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO IL
752 PM CST SAT FEB 13 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0745 PM     SNOW             HARVARD                 42.42N 88.62W
02/13/2021  M1.8 INCH        MCHENRY            IL   PUBLIC

            RELAYED VIA SOCIAL MEDIA.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO IL
753 PM CST SAT FEB 13 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0753 PM     SNOW             HAWTHORN WOODS          42.22N 88.05W
02/13/2021  M2.2 INCH        LAKE               IL   PUBLIC

            RELAYED VIA SOCIAL MEDIA.

&&